1. Field of the Invention
This invention relates to a method and system for evaluating a gloss and brightness character of a coated paint film, and more particularly to such a method and system for obtaining a numerically estimated total evaluation value for the gloss and brightness character which value is in good correlation to an organoleptic value for the gloss and brightness character.
2. Description of the Prior Art
Hitherto, evaluation of a gloss and brightness character of a coated paint film has been usually accomplished by using a device which mainly functions organoleptically under eye observation, as disclosed for example in a Japanese Utility Model Publication No 41-19039. An example of such a gloss and brightness evaluation device will be illustrated with reference to FIG. 1. In this evaluation device, when a switch 9 is turned on, a light bulb 10 is lighted to lighten a test pattern 11. Then light from the test pattern 11 is reflected by mirrors 12, 13, 14 and enters an eye glass 15. Thus, the reflected image of the test pattern 11 is observed by an observer whose eye only is shown in FIG. 1. As shown, a specimen plate 16 coated with a paint film is put in a light path from the test pattern 11 to the eye glass 15. The entry angle .theta. of light to the paint-coated specimen plate is 35 degrees, and the length l of a range in which the light enters is 50 mm.
Observation is accomplished by looking the image of the test pattern 11 through the eye glass 15. The gloss and brightness character is evaluated from deformation of the image of the test pattern 11. The test pattern 11 is provided with aligned large to small letters. The gloss and brightness of the coated paint film are higher as the smaller letters can be read by the observer.
The thus arranged gloss and brightness character evaluation device is arranged to evaluate the gloss and brightness of the coated paint film depending upon capability of reading the letters in the test pattern. Accordingly, the gloss and brightness character evaluation device has the following disadvantages:
(1) The observation result is unavoidably largely affected by the visual acuity of the observer. In other words, the observation result is largely affected by the deterioration degree in eye-ball focal distance control function which usually deteriorates with the observer's ages over 20 years old. The influence of such a deteriorated focal distance control function cannot be covered.
(2) The smoothness feeling and the gloss feelings as constituting elements of the gloss and brightness character can be totally evaluated but cannot be independently evaluated.
(3) The thickness feeling as an important constituting element of the gloss and brightness character cannot be evaluated.
(4) In case the surface condition of the coated paint film is considerably good, distinction in surface condition becomes difficult so as to provide the same evaluation value even among different samples.
In view of the above, establishment of the gloss and brightness evaluation method correlating well to visual observation has been eagerly desired.
Under such circumstances, it has been proposed to evaluate the gloss and brightness character of the coated paint film without depending upon visual observation and by using a gloss and brightness measuring device which is for example disclosed in Japanese Patent Provisional Publication No. 52-138960. The gloss and brightness character measuring device is illustrated with reference to FIG. 2. In this device, incidence of parallel beam of light is made to impinge on the surface of an object 20 to be measured at an entry angle of 45 or 60 degrees, under the effect of an optical system including a light source 17, a slit 18 and a lens 19. The light beam is reflected on the surface of the object 20 and scattered in accordance with the surface roughness condition of the object 20. The reflected and scattered light beam is concentrated on the surface of a pattern 21 and measured optically in degree of brightness by using a light receiving device 22, thus obtaining a gloss and brightness character value C which is given by the following equation: ##EQU1## where M is the maximum value of transmitted light in a lighted part of the pattern 21; m is the minimum value of the transmitted light in a dark part of the pattern 21.
However, with such a gloss and brightness character measuring device, the constituting elements of the gloss and brightness character cannot be independently evaluated. As a result, appropriate and desirable evaluation cannot be made in case the constituting elements of the gloss and brightness character are different among objects or in case concepts to be expressed are different among objects, i.e., when the thickness feeling and/or the smoothness feeling are particularly emphasized.